Unsteady heat transfer during the turbulent combustion of a lean premixed methane-air flame: Effect of pressure and gas dynamics

摘要

The objective of this work is to investigate the experimental behaviour of wall heat losses according to pressure and gas dynamics. Another goal is to improve the knowledge of unsteady flame-wall interaction. In a constant volume chamber, turbulent combustion occurs in a tumbling charge of lean methane-air mixture at equivalence ratio 0.7. Heat flux is calculated from wall surface temperature, and velocity is obtained by high-speed Particle Image Velocimetry. At first order, the low-frequency time evolution of heat flux is that of pressure. High-frequency time variations of heat flux are attributed to the cyclic fluctuations of large-scale velocity. As for large-scale velocity, its magnitude influences heat losses as well as its direction relatively to the wall. Compared to large-scale velocity, turbulence seems to have only second order effects on heat losses, in the case of a structured flow motion. Finally, the observed tendencies are in good agreement with previous results from thermal correlations and with laminar flame quenching measurements.